1. Field of the Invention
This invention relates to a coupler for bucket excavators, and which is provided with a special hook. The invention also extends to the construction of the hook.
2. Description of the Related Art
Hydraulically operated mechanical excavators have a dipper arm on the end of which are two mounting points by means of which an excavating bucket is pivotally attached to the end of the arm, and pivoted relative to the arm, respectively. Until relatively recently, if the operator wished to change the bucket, e.g. to a larger one, this had to be done manually. This involved the operator leaving the cab of the excavator, removing two pivot pins by means of which the bucket is connected to the dipper arm, getting back into the cab to lift the dipper arm clear of the bucket, aligning the dipper arm with the new bucket (and aligning the pivot apertures), de-mounting from the cab again, and locating the pivot pins in the aligned apertures, and securing them in place (e.g. with circlips, locking pins or bolts or the like) and then getting back into the cab to use the excavator. Sometimes, the operator would have considerable difficulty in removing or re-inserting the pivot pins, due to slight misalignment of the pivot apertures, and would have to use a heavy hammer for this purpose.
More recently, this time consuming exercise has been largely dispensed with, with the introduction of quick couplers which are located between the dipper arm and the bucket. The couplers can either be of the hydraulic type or of the mechanical type and are effectively permanently fitted to the two pivot aperture of the dipper arm and the bucket pivoting link, respectively. These couplers incorporate a generally horizontally and rearwardly extending hook-like aperture or jaw adapted to engage with one of the pivot pins on the bucket (both of which are left fitted to the bucket), and a generally downwardly extending aperture or jaw adapted to locate over the other pivot pin on the bucket, with which downwardly extending aperture a moveable latching hook is associated. See, for example, GB 2205299-A (Balemi). Another coupler is disclosed in U.S. Pat No. 5,692,325.
In manual versions of these couplers, the latching hook is biased by a coil spring to its latching position, and is moved away from its latching position by a release handle or lever rod which is removably locatable in an aperture in the nose of the latching hook.
In the hydraulic versions, a double acting hydraulic piston and cylinder device moves the latching hook between its respective positions, and a check valve is located within the piston and cylinder device to prevent inadvertent movement of the piston in the event of hydraulic failure.
However, in both the manual and hydraulic versions, a safety pin has to be provided which must be located by the excavator operator in specially provided aperatures in the coupler, to lock the latching hook in its latching position. This means that in both of these versions, the digger operator still has to leave his cab to secure in position the safety pin; this is inconvenient and time consuming.
In the known couplers, the hook has a profile which is such that, if the check valves fail and the hook: is carrying the weight of the bucket, the forces acting on the support pivot pin in the coupler are such that there is a moment about the pivot pin supporting the hook which will cause the hook to rotate to its unlatched position, thus releasing the bucket.
It is an object of the present invention to provide a fully automatic coupler for an excavator bucket which has a special coupler hook which will not rotate to a release position when under load and which can be operated by the excavator operator from his cab and which does not require the fitting of a safety pin by hand. Thus the operator does not have to leave the cab to change buckets.
According to the present invention, as defined in claim 1, we provide a coupler to enable an excavator operator to couple an excavator bucket to a dipper arm of an excavator without the leaving of the excavator cab, the coupler being locatable, in use, between the bucket and the dipper arm and having two spaced plates with two apertures therein by means of which it can be coupled by pins to the dipper arm and bucket pivot link of the excavator respectively, a first open-ended hook-like aperture in the plates extending generally horizontally and rearwardly for engagement, in use, with a first pivot pin provided on an excavator bucket, a latching hook pivotally supported on the plates for latching engagement in use with a second pivot pin provided on the bucket once the first hook-like aperture has been engaged with the first pivot pin and power operated means for moving the latching hook, operable, in use, by the operator from the cab, said latching hook having an internal concave surface with a profile such that when the hook is carrying the weight of the bucket via the second pivot pin, there will be a moment on the latching hook tending to cause it to move to a latching position.
Preferably, said latching hook has a profile such that, in use, when the hook is carrying the weight of the bucket via the second pivot pin, the pin will move along the internal concave surface of the hook, from a first position tending to unlatch the hook, to one putting no unlatching force on the hook and thereafter to one tending to move the hook to a latching position.
For this purpose, the free end of the hook preferably has an upturned, extended nose, the inner face of which is concave and which is preferably connected to the normal concave internal surface of the hook by an internal planar portion.
In the hydraulic version, although the piston and cylinder device for the latching hook is provided with a check valve and the special latching hook is provided, it is important that maximum provision is made to ensure that a bucket cannot accidentally become disconnected from the coupler, and preferably therefore, the coupler is also provided with blocking means adjustably supported on the coupler. This may be moveable under its own weight by the force of gravity into a blocking position in which it prevents the latching hook from being disengaged from the second pivot pin on the bucket, in which case the blocking means further includes resiliently deformable means on the blocking means which, in use, will engage an abutment when the coupler is inverted (with the result that the blocking means will tend under its own weight to move away from its blocking position), such engagement resulting in the resiliently deformable means biasing the blocking means into its blocking position.
Preferably, the latching hook is operated by means of a double acting piston and cylinder device, one end of which is pivotally connected about a first pivot axis to the coupler, and the other end of which is pivotally connected to the latching hook.
In one construction, the blocking means comprises a bifurcated blocking bar, the two limbs of which are pivotally supported on the coupler, preferably on the said first pivot axis, and the opposite end of which bears against a face on the rear of the latching hook.
In another construction, the blocking means may comprise a single blocking bar pivotally supported at one end region on the coupler, preferably on the first pivot axis and adapted to bear at its opposite end against a face on the rear of the hook.
Preferably, the face is stepped so that the coupler can be used with different sized bucket pivot pin distances (known as pin spread).
Preferably, the resiliently deformable means comprises an upstanding resiliently deformable arm on the blocking bar which will bear against an abutment on the dipper arm when the coupler is inverted, e.g. when a bucket operating cylinder is retracted to pivot the bucket.
Preferably, a protection plate is fitted over the latching hook and blocking means, through which plate the resiliently deformable arm projects, the plate being provided to ensure that excavated material does not interfere with the operation of the blocking means. The plate may be welded or bolted in position. Hydraulic hoses for the double acting piston and cylinder device for operating the latching hook may pass through one or more apertures in the plate; alternatively the plate carries two hydraulic hose couplings, and on the inner side of the plate, the couplings are permanently connected by suitable hoses to the said piston and cylinder device. This allows further hoses leading from the main pressure system on the excavator to be connected and disconnected easily to the coupler.